Reaction of carbonyl fluoride with fluorine



United States Patent Office 3,230,264 Patented Jan. 18, 1966 3,230,264REACTION OF CARBONYL FLUORIDE WITH FLUORINE Roger S. Porter, Orinda,Calif., and George H. Cady, Seattle, Wash., assignors, by mesneassignments, to the United States of America as represented by theSecretary of the Navy No Drawing. Filed Nov. 29, 1962, Ser. No. 241,0894 Claims. (Cl. 260-610) This application is a continuation-in-part ofour copending application Serial Number 838,3 89, filed September 8,1959, now US. Patent No. 3,100,803, issued August 13, 1963.

This invention relates to the preparation and production, by thereaction of carbonyl fluoride with fluorine, of perfluorodirnethylperoxide, a compound of the empirical formula, C F O The structuralformula probably is The object of the invention is to provide a goodmethod for producing the compound.

It has heretofore been known that perfluorodirnethyl peroxide isproduced in small yield by the electrolysis of an aqueous solutioncontaining trifluoroacetate ion [F. Swarts, Bull. soc. chim. Belg, 42,102 (1933)] but only very small amounts have been obtained. The methodis costly because of the low efliciency in utilization of materials. Thepresent invention users materials etficiently and is capable ofproducing large amounts of perfluorodimethyl peroxide at a much lowercost than was formerly possible.

Perfluorodimethyl peroxide is an oxidizing agent capable of supportingthe combustion of hydrocarbons and other fuels. It is of potential valueas an oxidant for fuels in rocket propulsion. Since it is a peroxide, itmay be expected to be of value for causing polymerization reactions tooccur.

The inventors now disclose that perfluorodirnethyl peroxide is formed bycombining carbonyl fluoride with trifluoromethyl hypofluorite. Thereaction may be represented by the equation:

They also disclose that the peroxide may be prepared by combiningfluorine with carbon monoxide or with carbonyl fluoride. Fluorinatingcatalysts such as the higher fluorides of metals belonging to the classincluding AgF CuF C01 CeF HgF SbF FeF and NiF induce the reaction. Inthe case of carbonyl fluoride, it is probable that fluorine reacts togive trifluoromethyl hypofluorite as shown in Equation 2 and that thehypofluorite combines with unchanged carbonyl fluoride as shown inEquation 1. When carbon monoxide is used as the starting material, itfirst reacts with fluorine to give carbonyl fluoride as shown inEquation 3 The carbonyl fluoride may then give perfluorodirnethylperoxide by Reactions 2 and 1. These equations and the theoreticaldiscussion are given-at this point to make clear the nature of theinvention and to show that the different methods may be regarded as oneinvention.

The theory permits one to predict that many substances may react withfluorine to give perfluorodirnethyl peroxide. Thus, one would expect anysubstance capable of reacting with fluorine to give carbonyl fluoride toalso be capable of giving perfluorodirnethyl peroxide. It should bepossible to prepare perfluorodirnethyl peroxide by the reaction offluorine with such substances as methanol, ethanol, dimethyl ether,formaldehyde and many other compounds containing carbon and oxygenatoms. Many com-binations of reactants should give both carbonylfluoride and trifluoromethyl hypofluorite. When both of these productsare present in a reacting mixture, one may expect to obtainperfluorodirnethyl peroxide. Perfluorodimethyl peroxide can be producedby reacting carbon monoxide, carbon dioxide or carbonyl fluoride witheither fluorine or trifluoromethyl hypofluorite.

In order that a high yield of perfluorodirnethyl peroxide may beobtained by the reaction of fluorine with carbonyl fluoride or carbonmonoxide, or by the reaction of carbonyl fluoride with trifluoromethylhypofluorite, it is necessary that the temperature and the relativeproportions of the reactants be held within certain limits. The yieldalso is dependent upon the length of time allowed for the reaction andupon the presence or absence of a catalyst.

Four different reaction vessels have been used by the inventors toprepare perfluorodirnethyl peroxide. Vessel A was a cylindricalcontainer made of nickel. It had a volume of 1.71 liters and it could beheated to any desired temperature by electrical heaters. Its temperaturewas measured by thermocouples. The reactants were added separately tothis vessel and their pressures were measured. As the vessel was heated,the course of a reaction involving a pressure change was followed bymeasuring the total pressure of the mixture of gases. Samples of gaswere sometimes removed from the vessel for identification and analysis.

The second reaction vessel (vessel B) was constructed of copper tubing.It was used to study reactions under conditions of continuous flow. Thetwo gaseous reactants entered (by separate inlets) a cylindrical mixingchamber having an internal diameter of 4.1 cm. and a length of 9.0 cm.They passed through this chamber and then through an electrically heatedtube of 89 cm. length and 1.7 cm. internal diameter. When carbonmonoxide and fluorine were used as the reactants much heat was liberatedin the mixing chamber. If rapid flows of these gases were to be used ina large scale plant, it would be desirable to cool the reactor near theinlets for reactants.

A third reaction vessel (vessel C) was also constructed from coppertubing. It was packed with a tangled mass of copper ribbon of 0.035 cm.width and 0.008 cm. thickness. This ribbon weighed 4500 g. and beforeuse, it was plated with 100 g. of silver. As the result of use, thesilver metal became converted to fluorides of silver. The reactionvessel had a length of 90 cm. and an internal diameter of 7.5 cm. Itcould be heated by passing electricity through coils of resistance wirewound over a layer of asbestos paper surrounding the reactor. There weretwo heating coils. This made it possible to control the temperatureseparately in each end of the reactor. At one end of the reactor the twogaseous reactants entered, each by its own inlet, and at the other endthe products departed through an outlet.

The fourth reaction vessel (vessel D) was a steel cylinder of the typecommonly used to store gases. Its capacity was approximately fiveliters. Its inner surface was conditioned by long exposure to fluorine;then the cylinder was used in the laboratory as a storage tank fortrifluoromethyl hypofluorite, CF OF.

When using each type of apparatus it was possible to collect samples ofthe products by condensing them in traps cooled by liquid oxygen. Suchsamples were analyzed by distillation, the substances being recognizedby their boiling points and other properties.

Example 1.Equimolar amounts of trifluoromethyl hypofluorite and carbonylfluoride were placed in vessel A at 27 C. giving a total pressure of16.1 cm. of mercury.

The vessel was heated slowly to 287 C. Up to 225 C. the pressureincreased in proportion to the absolute temperature, thereby indicatingnot more than a little combination of the two gases. Above about 235 C.the pressure decreased with rising temperature, thereby indicating thatthe gases were combining. When the vessel was returned to 27 C. thetotal pressure of gas was 11.1 cm. of mercury. The remaining gas wasfound to contain perfluorodimethyl peroxide together with unreactedtrifiuoromethyl hypofluorite and carbonyl fluoride. The decrease inpressure corresponded to the conversion of 62% of the reactants toperfluorodimethyl peroxide. This experiment showed that the rate ofreaction of trifiuoromethyl hypofluorite with carbonyl fluoride becameappreciable at about 230 C. It also showed that the rate increased withrising temperature above 230 C. (as indicated by an increase in the rateof pressure change). Since the reaction was slow in the neighborhood of230 C. to 250 C., it follows that the duration of contact of thereactants in a continuous flow reactor at this temperature is importantin determining the yield of perfluorodimethyl peroxide.

Vessel A was also used to study the decomposition of perfluorodimethylperoxide. A sample of the gas was heated slowly to 420 C. At about 225C. the substance started to decompose, as shown by an abnormally greatincrease in pressure with temperature. At approximately 325 C. thedecomposition was substantially complete. This experiment shows that itis desirable when preparing perfluorodimethyl peroxide to keep thetemperature of the reactants as low as possible while still obtainingthe desired product. When a continuous flow reactor is used attemperatures above 325 C., one may obtain perfluorodimethyl peroxide,but it is probable that much of the product is formed as the temperatureof the gas falls, upon leaving the reactor.

Example 2.-Several runs were made using reaction vessel B to determinethe effect of temperature and of the relative concentrations of thereactants upon the yield of perfluorodimethyl peroxide. Carbon monoxideentered one inlet and fluorine the other. The total pressure within thesystem was substantially one atmosphere. The reaction conditions and theyield of perfluorodimethyl peroxide are given in Table 1. The yield of CF O shown in column 5 was calculated from the equation: yield wt. ofcarbon in C F O produced (3) When the ratio of F to CO was greater than2 to 1, much CF OF was formed but little C F O (see Runs 3 and 7). (4)If the ratio of F to CO were to be 1 to 1 or less, nearly all of theproduct probably would be COF (see Run 8).

The greatest yield of perfluorodimethyl peroxide obtained fromcontinuous gas streams through vessel B was about 21% of thattheoretically possible. The yield was independent of temperature from307 C. up to the highest temperature used, 405 C. Since Example 1indicated that the peroxide should not have been obtained above about325 C., it is likely that the perfluorodimethyl peroxide obtained withvessel B at its higher temperatures was formed as the gas became coolerwhile passing through the outlet tube leading from the reactor.

Runs 11 and 12 of Table 1 showed that carbonyl fluoride was formed fromfluoride and carbon monoxide when the temperature of the reactor washeld below about 200 C. but that the formation of perfluorodimethylperoxide must have been very slow. Unreacted fluorine remained mixedwith the carbonyl fluoride. When no electrical heating of the reactorwas used, it was possible to tell that the reaction to form carbonylfluoride occurred in the mixing chamber. This became warm to the touch(perhaps C.) but the tube of 89 cm. length remained at about 25 C. Runswhich produced perfluorodimethyl peroxide must have done so by thereaction of carbonyl fluoride with fluorine in the heated tube of vesselB. This series of experiments showed that perfluorodimethyl peroxide wasproduced by the reaction of fluorine with carbon monoxide or withcarbonyl fluoride. The best yields of perfluorodimethyl peroxideresulted from using COF and F in a volume ratio of 2 to 1 as required bythe net equation Example 3.--Vessel C was used, the region near the gasinlets being at C. and the region near the outlet being at about 183 C.Fluorine was passed at a rate of 3.25 liters per hour and carbonmonoxide at 2.20 liters per hour (each measured at about 25 C. and oneatmosphere pressure). The yield of perfluorodimethyl peroxide was about58% of that theoretically possible from the amount of carbon monoxideconsumed. Both carbonyl fluoride and trifiuoromethyl hypofluorite wereobtained as by-products. In another run in vessel C the top half of thevessel was not heated but the temperature near the outlet was maintainedat about 86 C. Rates of flow of gases in liters per TABLE 1.-PREPARATIONOF PERFLUORODIMETHYL PEROXIDE IN VESSEL B Rates of Flow, liters per hourat room temp. and

pressure Yield, 021 0 2.

Run No. percent GO F Other products: n1=much,

'ttle 1 In run 12 the reactor was filled at room temperature by passingF2 and CO at rates of 3.20

At the end of this Neither OZFGOE nor OFJOF were observed to be hour at25 C. and one atmosphere were: F 3.30; CO, 2.15; N (diluent) 4.0. When asample of the product was distilled CF OOCF had been produced at a rateof about 2.0 grams per hour. In still another run made in vessel C noelectrical heating was used. The temperature near the inlet was about 50C. and near the outlet was (4) 75 about 27 C. Rates of flow of gasesmeasured in liters per hour at about 25 C. and one atmosphere were: F2.90; CO, 2.15; N (diluent), 4.0. When a sample of the product wasdistilled, no perfluorodimethyl peroxide was found. A small amountprobably was present. If so, however, it distilled with the carbonylfluoride. The gas contained fluorine and much carbonyl fluoride. In thecase of this run the gas streams were shut off and the mixture wasallowed to stand in the apparatus at about 25 C. for 23 hours. A sampleof the gas was then removed. The produce contained CF OF, COF andperfluorodimethyl peroxide approximately in the volume ratio: 2 to 5 to8 respectively.

The runs in Example 3 showed that the first step in the process was theproduction of carbonyl fluoride as shown in Equation 3 and that this wasfollowed by additional reactions involving fluorine, to givetrifluoromethyl hypofluorite and perfluorodimethyl peroxide. By usingvessel C it was possible to produce perfluorodimethyl peroxide attemperatures as low as 25 C. With vessels A and B temperatures near 200C. or more were required for the reaction to proceed rapidly. It followsthat vessel C contained a catalyst for the formation ofperfluorodimethyl peroxide and that the catalyst was the tangled mass ofcopper ribbon bearing a surface layer formed by the fluorination ofsilver.

Example 4.Trifluoromethyl hypofluorite was stored at room temeprature invessel D for a period somewhat over one year. At first the gas containedsome carbonyl fluoride as an impurity but little or no perfluorodimethylperoxide was present. At the end of the storage period a part of the gaswas condensed and distilled. An appreciable amount of perfluorodimethylperoxide then was present. This example shows that trifluoromethylhypofluorite and carbonyl fluoride react even at room temperature toform perfluorodimethyl peroxide. From Examples l and 2 it is evidentthat the reaction at room temperature (about 25 C.) is very slow.

Summary.--(l) Perfluorodirnethyl peroxide may be obtained in thefollowing ways: (a) combining carbonyl fluoride with trifluoromethylhypofluorite, (b) combining carbon monoxide with fluorine, (c) combiningcarbonyl fluoride with fluorine, (d) reacting carbon dioxide withfluorine. Any combination of reactants which forms both carbonylfluoride and trifluoromethyl hypofluorite should also be capable offorming perfluorodimethyl peroxide.

(2) The preferred proportions of reactants are in each case thoserequired by the stoichiometry of the reactions. A range ofconcentrations may be used in each case. For carbon monoxide andfluorine it is best that the ratio by volume lie within the limits 1 to1 up to 1 of CO to 2 of F For fluorine and carbonyl fluoride it isdesirable that the ratio of F to COF be less than 1.

(3) In the absence of a catalyst the reaction vessel should preferablybe held at a temperature greater than 200 C. The reaction occurs attemperatures as low as 25 C. but it is slow. Even thoughperfluorodimethyl peroxide decomposes at temperatures below 325 C., itis possible to produce the substance with the reactor (at least in part)at higher temperatures than this. Apparently the upper temperature limitis that at which the rate of corrosion of the reaction by fluoriinebecomes large. For a nickel vessel this temperature is about 500 C.

(4) Copper, coated with silver fluoride(s) serves as a catalyst for thepreparation of perfluorodimethyl peroxide. When it is present, reactiontemperatures as low as 25 C. may be used. Example 4 shows that thecatalyst is not necessary, even at temperatures as low as about 25 C.The catlayst can be used over the entire temperature range suitable forthe preparation of perfluorodimethyl peroxide. The preferred portion ofthis temperature range wherein the yield of the product is of desirablemagnnitude is from about C. to about 325 C. and it is in that segment ofthis preferred portion of the temperature range lying between about 80C. and about 225 C. that the catalyst is very helpful, because below 225C. the reaction of CF OF with COF is otherwise undesirably slow.Although the catalyst can be used in the higher segment, from about 225C. to about 325 C., of the preferred portion of the temperature range,the reaction proceeds in that segment of the temperature range at apractically desirable rate in the asbence of a catalyst, as suggested in(3) immediately above.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A process of producing perfluorodimethyl peroxide which comprisesintroducing carbonyl fluoride and fluorine into a reaction zone andreacting them at a temperature of at least 25 C., the volume of carbonylfluoride used being greater than the volume of fluorine.

2. A process as defined in claim 1 in which the temperature is withinthe range 225 C. to 325 C.

3. A process as defined in claim 1 wherein there is present a catalystcomposed of fluorides of metals selected from the group consisting ofsilver, copper, cobalt, cerium, mercury, antimony, iron, nickel.

4. A process of producing perfluorodimethyl peroxide which comprisesintroducing carbonyl fluoride and fluorine into a reaction zone andreacting them in the presence of a catalyst and within the temperaturerange, 80 C. to 225 C., the volume of carbonyl fluoride being more than1.33 and less than 4.0 times as great as the volume of fluorine, saidcatalyst being composed of fluorides of metals selected from the groupconsisting of silver, copper, cobalt, cerium, mercury, antimony, iron,nickel.

References Cited by the Examiner UNITED STATES PATENTS 3,100,803 8/1963Porter et a1 260-610 OTHER REFERENCES Porter et al., J our. Amer. Chem.Soc., 79:5628-31 (1957), 4 pp.

LEON ZITVER, Primary Examiner.

HAROLD G. MOORE, Examiner.

1. A PROCESS OF PRODUCING PERFLUORODIMETHYL PEROXIDE WHICH COMPRISESINTRODUCING CARBONYL FLUORIDE AND FLUORINE INTO A REACTION ZONE ANDREACTING THEM AT A TEMPERATURE OF AT LEAST 25*C., THE VOLUME OF CARBONYLFLUORIDE USED BEING GREATER THAN THE VOLUME OF FLUORINE.